There are known distributing devices for machines of this type which are used for injection molding by the low-pressure process. In one of them, the foamable polymer melt streams are controlled by a rotating three-position valve or two two-position valves, while in machines for molding by the gas counter-pressure method there is also used a distributing device, which is disposed between an accumulating cylinder, the injection mold and the plasticating unit this device comprising a non-return valve between the plasticating unit and the accumulating cylinder.
A drawback of these known distributing devices for machines of this type lies in that, because of the direct connection between plasticating unit, mold and accumulating cylinder, there is the possibility that not only fresh or virgin plasticated material will be introduced into the mold, but also material already foamed during the previous cycle before the formation of a skin, thus impairing the quality of the latter. Another drawback lies in the necessity of separate devices for the actuation and control of the valves.